1. Field of the Invention
The present invention relates to an apparatus and a method of driving an optical pickup actuator, and more particularly, to an apparatus and a method of driving an optical pickup actuator in which a focus coil, a track coil, and a tilt coil which drive an optical pickup in a focus direction, a track direction, and a tilt direction, respectively, are provided at both sides of a bobbin to secure the remaining sides of the bobbin, and the focus coil is also used as the tilt coil.
2. Description of the Related Art
In general, optical pickups are adopted in optical recording/reproducing apparatuses. An optical pickup performs recording and/or reproduction of information with respect to a recording medium, such as an optical disk, placed on a turntable in a non-contact manner while moving in a radial direction of the optical disk.
The optical pickup includes an objective lens which forms a light spot on the optical disk by focusing light emitted from a light source, and an actuator which controls the objective lens in a track direction, a focus direction, and a tilt direction so as to accurately place the light spot formed by the objective lens on the optical disk.
The optical pickup actuator includes a double axes driving actuator which drives the optical pickup in the track direction and the focus direction. Recently, to perform a high density recording, the N/A of the objective lens has been increased and the wavelength of a laser has been decreased. However, a margin in tilt of the optical pickup actuator decreases in response to increase of the N/A and decrease of the wavelength. To compensate for the reduced tilt margin, three axes or four axes driving actuators capable of driving an optical pickup in the tilt direction are needed in addition to the existing double axes driving actuator. The three axes driving refers to driving in the focus direction, the track direction, and the tilt direction. The four axes driving refers to driving in the focus direction, the track direction, a tilt radial direction, and a tilt tangential direction. Referring to FIG. 1, the focus direction, the track direction, the tilt radial direction, and the tilt tangential direction are indicated by L-Lxe2x80x2, M-Mxe2x80x2, N, and O, respectively.
FIG. 1 shows a conventional optical pickup actuator which includes a base 100, a holder 103 fixed to the base 100, a bobbin 107 where an objective lens 105 is mounted, wires 109 which connect the bobbin 107 to the holder 103, and a magnetic driving portion (described below) which moves the bobbin 107 in the track direction, the focus direction, or the tilt direction.
The magnetic driving portion includes a couple of a focus coil 110 and a tilt coil 112 (see FIG. 2A) provided at each of the opposite side surfaces 107a of the bobbin 107, a track coil 115 arranged at each of the other side surfaces 107b where the focus coils 110 and the tilt coils 112 are not arranged, and first and second magnets 117 and 119 installed on the base 100 to face the focus coils 110, the tilt coils 112, and the track coils 115 with corresponding predetermined intervals therebetween. Outer yokes 118 and 120 which fix the first and second magnets 117 and 119 are installed on the base 100. Inner yokes 122 are installed on the base 100 at corresponding positions facing the first magnets 117 to guide the bobbin 107. The outer yokes 118 and 120 and the inner yokes 122 guide a path of magnetism generated by the first and second magnets 117 and 119 to direct the bobbin 107 to a desired location.
Each of the wires 109 has one end soldered to a corresponding area of both the opposite and other side surfaces of the bobbin 107 and the other end connected to the holder 103, and is electrically connected to a circuit portion (not shown) which applies current to the magnetic driving portion.
FIG. 2A shows an example of the polarity of the first magnet 117 and the direction of current I to disclose the relationship of forces by the interaction between the focus coil 110 and the tilt coil 112, and the first magnet 117 corresponding thereto. Here, the focus coil 110 provided at each of the opposite side surfaces 107a of the four side surfaces of the bobbin 107 receives a force Ff by Fleming""s left hand rule so that the bobbin 107 is moved in the focus direction L. Where the direction of the current I changes to the opposite, the focus coil 110 receives a force in the opposite direction Lxe2x80x2.
The tilt coil 112 is provided at both opposite side surfaces 107a of the bobbin 107, forms a couple with the corresponding focus coil 110, and interacts with the corresponding first magnet 117. Here, where the same currents flowing in the opposite directions are applied to the tilt coils 112, the forces Fti received by the both tilt coils 112 become opposite so as to drive the optical pickup in the tilt direction, in particular, in the radial tilt direction (N).
FIG. 2B shows an example of the polarity of the second magnet 119 and the direction of current I to disclose the relationship of forces by the interaction between the track coil 115 and the second magnet 119 corresponding thereto. The direction and magnitude of forces between a magnet and a coil is determined by Fleming""s left hand rule. Thus, the track coil 115 provided at each of the other side surfaces 107b of the four side surfaces of the bobbin 107, where the focus coils 110 and the tilt coils 112 are not arranged, receives the force Ft in the track direction by the second magnet 119 so as to move the bobbin 107 in the track direction M. Here, where the direction of current I changes to the opposite, the track coil 115 receives a force in the opposite direction Mxe2x80x2.
Typically, six wires 109 of the optical pickup actuator are provided to drive the bobbin 107 in the focus direction, the track direction, and the tilt direction. But, more wires may be needed for a four axes driving actuator.
However, since the optical pickup actuator is very small, where all four side surfaces of the bobbin 107 are used to install the focus coils 110, the track coils 115, or the tilt coils 112, a sufficient space may not be present to install the wires 109. In addition, when the number of the wires 109 increases, it is very difficult to attach the additional wire(s) in such a small space. Accordingly, the defective ratio of the conventional optical pickup actuators increases.
Also, when coils are arranged using all four side surfaces of the bobbin 107, wiring of the coils is complicated. Furthermore, since a magnet is provided at each of the focus coil 110, the tilt coil 112, and the track coil 115, the number of parts constituting the optical pickup actuator increases, decreasing the productivity. Additionally, interference with a spindle motor (not shown), which rotates a disc, is generated by the first magnet 117 arranged at the opposite side surfaces (left and right sides) of the bobbin 107. Therefore, the spindle motor is not accurately controlled.
Accordingly, it is an object of the present invention to provide an apparatus and a method of driving an optical pickup actuator in which a focus and tilt coil and a track coil which drive an objective lens in the focus direction, the track direction, and the tilt direction are arranged at both side surfaces of a bobbin so as to secure a sufficient space provided at the other side surfaces of the bobbin, wherein driving in the focus direction and the tilt direction can be controlled together by a single coil.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a method of driving an optical pickup actuator having a bobbin, a support member, focus and tilt coils, track coils, and magnets, the method comprising arranging the bobbin on a base of the optical pickup actuator so as to be moved by the support member, installing at least one focus and tilt coil to drive the bobbin in focus and tilt directions and at least one track coil to drive the bobbin in a track direction at each of opposite side surfaces of the bobbin, arranging the magnets to face the respective focus and tilt coils and the track coils, and dividing the focus and tilt coils into at least two sets of coils and applying an input signal to each of the sets.
According to an aspect of the present invention, the installation of at least one focus and tilt coil comprises arranging first and third focus and tilt coils on one side of the opposite side surfaces of the bobbin, and arranging second and fourth focus and tilt coils on the other side of the opposite side surfaces of the bobbin. The applying of the input signal comprises inputting first and second input signals to respective first and second set coils, wherein each of the first and second set coils is formed by a coupling of two of the first through fourth focus and tilt coils.
The first set coil may be formed of the first and third focus and tilt coils and the second set coil may be formed of the second and fourth focus and tilt coils. Alternatively, the first set coil may be formed of the first and second focus and tilt coils and the second set coil may be formed of the third and fourth focus and tilt coils.
The first and second input signals may be the same input signal to drive the bobbin in the focus direction. Alternatively, the first and second input signals may have different phases. On the other hand, each of the first and second input signals may comprise a sum signal of a focus signal and a corresponding tilt signal having a phase different from that of the focus signal.
Each of the magnets may have four polarizations. Alternatively, each of the magnets may comprise first magnet and second magnet parts, each part having two polarizations.
The method of driving the optical pickup actuator further includes inputting another input signal to each of the track coils independent of the focus and tilt coils.
At least one of the focus and tilt coils and the tracks may be formed of a fine pattern coil.
The support member may be arranged at other opposite side surfaces of the bobbin, wherein the focus and tilt coils and the track coils are not arranged on the other opposite side surfaces of the bobbin.
To achieve the above and other objects according to another embodiment of the present invention, there is provided a method of driving an optical pickup actuator having a bobbin, a support member, focus and tilt coils, track coils, and magnets, the method comprising arranging the bobbin on a base of the optical pickup actuator so as to be moved by the support member, installing at least one focus and tilt coil to drive the bobbin in focus and tilt directions and at least one track coil to drive the bobbin in a track direction at each of opposite side surfaces of the bobbin, arranging the magnet to face the respective focus and tilt coils and the track coils, and independently inputting a signal to each focus and tilt coil.
The same input signal may be input to at least one of the focus and tilt coils to drive the bobbin in the focus direction.
A different input signal may be applied to at least one of the focus and tilt coils to drive the bobbin in the tilt direction.
The installation of at least one focus and tilt coil may comprise arranging first and third focus and tilt coils on one side of the opposite side surfaces of the bobbin, and arranging second and fourth focus and tilt coils on the other side of the opposite side surfaces of the bobbin. The applying of the input signal may comprise inputting first and second input signals to respective first and second set coils, wherein each of the first and second set coils is formed of a selected couple of the first through fourth focus and tilt coils.